Some processes for fabricating semiconductor devices on a substrate utilize plasma processing chambers in which a showerhead (for example) provided process gases to the processing chamber which may be ignited to form a plasma. Plasma processing, however, tends to increase the temperature of components inside the processing chamber, such as the showerhead. Moreover, for high RF power process conditions, the combination of plasma heating and the duration of the process step typically causes the temperature to undesirably overshoot a desired set point. Such temperature overshoots can impinge on the ability to strike plasmas, delay initiating semiconductor processing recipes, and degrade the quality of processing.
There are some ways to increase the cooling capacity of process chamber components to address the problem, such as to design new hardware to have better heat conductance, or to change the coolant temperature between idle mode and processing modes. However, such designs are undesirable due to inefficiencies and/or cost. For example, the time constant of typical heat exchangers or chillers is close to typical recipe times. Accordingly, merely lowering the coolant temperature will not enable heating of the tool at a constant temperature during idle mode unless a much larger heater is provided. However, implementation of such a design would requires a major tool redesign, as most of heaters are embedded in the tool body.
Thus, there is a need for improved methods and apparatus for heat control in a plasma processing chamber.